docs: def apply_mask(matrix, mask_pattern, matrix_size, is_encoding_region):
      """\
      Applies the provided mask pattern on the `matrix`.
  
      ISO/IEC 18004:2015(E) -- 7.8.2 Data mask patterns (page 50)
  
      :param tuple matrix: A tuple of bytearrays
      :param mask_pattern: A mask pattern (a function)
      :param int matrix_size: width or height of the matrix
      :param is_encoding_region: A function which returns ``True`` iff the
              row index / col index belongs to the data region.
      """
      for i in range(matrix_size):
          for j in range(matrix_size):
              if is_encoding_region(i, j):
                  matrix[i][j] ^= mask_pattern(i, j)